The microwave oven as a typical microwave heating appliance can heat directly the foods as a typical heated subject. Therefore, its convenience of needing no cooking pan or pot makes the microwave oven the appliance indispensable to life. Up to now, the microwave oven having a food loading space, width and depth dimensions of which is about 300 to 400 mm respectively and a height dimension of which is about 200 mm, of the heating chamber through which a microwave propagates is widespread commonly.
In recent years, the products having a heating chamber whose food loading space has a flat bottom surface and whose lateral width is widened by setting the width dimension to 400 mm or more relatively larger than the depth dimension such that a plurality of food plates can be heated to enhance its convenience are put to practical use.
By the way, it has been known that a wavelength of the microwave used in the microwave oven is about 120 mm, strong and weak electric field distributions (referred to as “field strength distributions” hereinafter) are caused in the heating chamber, and thus unevenness in heating is caused by a synergistic effect of such unevenness and influences of the shape of the heated subject and its physical property. In particular, in the above heating chamber having the large width dimension, uniformity of the heating must be increased rather than the prior art to heat simultaneously the foods put in plural dishes.
In the prior art, in this type microwave heating appliance, one radiation antenna is provided and is rotated and driven in operation, but it is difficult to heat locally a center area of the heating chamber. Therefore, as the measure of enhancing uniformity in heating, the microwave heating appliance equipped with a plurality of radiation antennas or a plurality of high-frequency stirring unit has been proposed (see Patent Literature 1).
However, the microwave heating appliance does not always heat a large amount of foods, although such heating appliance has a wide heating chamber. For example, when a mug of milk is warmed, it is effective to heat concentratedly the milk only, not heat uniformly the overall heating chamber.
Also, when a plurality of foods are heated at the same time, only the low-temperature food should be heated concentratedly in a situation that a difference resides in temperatures of the foods, for example, the frozen food and the room-temperature food should be heated simultaneously. In addition, like the variety box lunch, or the like, the foods not to be heated (pickles, salad, dessert, etc.) are contained in as one vessel. Therefore, often only the foods to be heated (boiled rice, side dishes, etc.) should be heated concentratedly.
In such case, a function of not heating uniformly the overall heating chamber but heating concentratedly the local area is needed. For this reason, the microwave heating appliance capable of heating concentratedly the heated subject by switching a plurality of antennas and controlling the stop position, and the like has been proposed (see Patent Literature 2).    Patent Literature 1: JP-A-2004-259646    Patent Literature 2: Japanese Patent No. 3617224